This invention concerns a method to shear slabs arriving from the continuous casting plant and the relative device.
The invention is applied in rolling lines associated with continuous casting machines and to be more exact in the section immediately after the outlet of the continuous casting machine.
In rolling mill plants, the slab as it leaves the continuous casting machine is sent to be sheared for size so as to prepare the sections which are speeded up and sent to be rolled.
The high temperature of the slab at this point causes conditions of great plasticity, and the slab is therefore easily deformed.
As it leaves the shearing means, during the intervals between the carrying and supporting rolls where there is no support, the leading end of the slab tends to bend downwards as a result of its own weight; the greater the distance between adjacent rolls, the greater is this tendency to bend.
This lowering of the leading end of the slab causes a great danger of the slab knocking against the carrying rolls and pinch rolls, which consequently causes damage both to the slab and the rolls.
This bending, when it is not obviated by the guide boxes for the rolled stock which are located upstream of the mill rolls, can even cause the slab to jam on the rolls themselves, which causes a blockage of the line and considerable problems to restart the line.
This problem moreover is particularly serious when it concerns the carrying rolls inside the tunnel furnace which is included downstream of the shearing means. The rolls inside the furnace, in fact, are made of fragile material, able to resist high temperatures and therefore more vulnerable to the mechanical stresses caused when they are knocked by the leading end of the slab.
When there are frequent knocks and blockages, there is therefore a quicker wear of the elements comprising the rolling train, particularly the rolls, and there is a greater possibility of damage and/or localised breakdowns. This implies a more frequent replacement or repair of the parts of the rolling mill and consequently an interruption in the production cycle with a resulting increase in maintenance costs and down times.
As a consequence of the knocks and blockages and therefore of the resulting mechanical stresses, the slab too is in a deteriorated condition when it enters the rolling train, which leads to imperfect working and in any case a poor quality product is obtained.